1986 Force 50 Return to Idle

[jwall116]

Hello iBoats !

I have a 1986 Force 50 that has an odd symptom hat I have no been able to make go away.

Rather in the water or on Muffs, when I bring the engine above idle in neutral it will not return to idle smoothly. Rather is is cold or warm it will after a certain point, maybe 1500 rpm, begins bucking and reving up despite the throttle being closed. Waiting it out if the revs do not get too high or turning off the ignition will stop it.

This sounds like run-away but it will do it even on first start. It has done it a hand full time right after start up at the boat dock. My idle when cold is about 1200-1300rpm, once warm this settles to around 900. I have decarbed the motor with a 1 gallon death mix, and have ran 2 cans of seafoam mixed in the 5 gallon tank. This engine has been ran atleast once a week in the water since purchased 6 months ago.

Plugs are new and do not load up, WOT is great, Compression COLD is 120PSI on both cyl, havent tested it warm. I run Penz 50:1 semi synthetic and 87 Oct pump gas with Marine Stabil on every tank no matter what. Engine always starts right up and runs great.

Idea's are welcome!

 

[Nordin]

Does it always do this even if it is warm and you start it without the coldstart procedure (knob out and throttle forward as far as it will go. This depends on what kind of remote you have)?
When it is warm it should start with remote in no coldstart position. Remote in neutral and the idlesetting should give you RPM about 750-800.

Two strokes will act like this when you run on muffs because of no backpressure for the exhaust. But as I understand you it act like this even in water.

I would start with cleaning the carb and then setting the throttle/timing sync correct and then setting the fuel/air mix screw (about 1-1,5 turn out from seated).
If this not solve the problem look at the timing. Does the timingplate retard smooth and back to right advance in idle when you go back to idle.
You set the timing with throttle in WOT and it should be 30 dgr BTDC.

 

[jwall116]

When I start cold, I use choke and the throttle at idle. I haven't had a need to use throttle to start ever.

The timing has never been messed with that I know of.

At the dock, the engine has does this only a few times. On the muffs it does it every time I rev it up past idle.

I like to clear the plugs during flushing/ allow engine to run at a fast idle. With this issue, I can not do that.

 

[Frank Acampora]

It sounds like the throttle cable quick-connect fitting is not adjusted correctly or is not the correct fitting. It should be a spring loaded quick connect about 2 1/2 inches long. The spring loading puts traction on the cable and ensures positive return to idle. Without it, the idle will fall where it may because of compliance in the cable--sometimes high, sometimes normal.

The quick- connect should be adjusted so that the center portion is pulled out 3/16 to 1/4 inch at idle. Do this by adjusting on the threaded portion of the cable end. To reattach to the ball fitting you will find it easier to put the engine in gear with the throttle opened slightly

 

[jwall116]

Hi frank

The idle always goes back where it belong. When I blip the throttle either with the controls in neutral or manually on the carb it self the engine goes into a run away sorta behavior. The only way to describe it would be a hammering deceleration. I will take video of this and upload.

 

[pnwboat]

You may be experiencing a "Lean Mixture" condition. When the motor goes into the run away type behavior, try hitting the choke for a second to see if that stops it. If it does, then you might want to check the carburetor......fuel mixture adjustment and or the fuel pump diaphragm. Make sure the primer bulb is working properly and all fuel lines in good condition.

 

[jwall116]

I agree that it is a lean condition. When I first purchased the boat at an off idle no wake speed the engine would misfire. I tuned the low speed needle richer about 1/8 turn and the problem went away.

I guess the big question is. Do I need to run the low end overly rich to make this stop or is this a carb issue. Previous owner said he rebuilt carb last year and engine starts right up every time.

 

[Frank Acampora]

The check is in the mail. I'll respect you in the morning. The engine ran when I put it away. I just rebuilt the carbs.

Caution Will Robinson, caution! Carbs are a critical part of these engines. Set incorrectly or run dirty and they will cause major damage. So many back yard and garage mechanics THINK they know what they are doing when they really don't have a clue.

Low speed circuits are linked with high speed circuits in these simple carbs and too lean a low speed setting will also lean the high speed resulting in detonation at or near full throttle.

THUS: It is in your best interest to remove the carbs, disassemble them and clean them before you run the engine again. Search the many threads on this forum about cleaning carbs, float setting, and low speed needle settings and get them right.

As with any used engine, ASSUME that nothing is set correctly and put everything back to factory specs before running.

 

[jwall116]

I have the manual for the engine so I will rebuild the carb tonight.

Will let the forum know soon what happens!

 

[jwall116]

I disassembled the carb, it was actually very clean. No varnish. I used a full can of carb cleaner through all passages and jets. The float height was ever so slightly off, so i adjusted that. Put back on the engine and it fired right up immediately. Tuned the low speed and the problem still shows its pretty face.

I can stop it's behavior by using the choke or hitting the key.

I took a video to show you what it is doing.

In the water, this isn't an issue So i will be boating tomorrow but I would like for this madness to be fixed.

 

[Nordin]

I have looked at the video and from my experience of OB this engine acts absolutly normal. If this behavior not appears in water on a boat......no problem.
As I stated previously in this thread 2 strokers need the right backpressur for the exhaust to run correct. And from the video this engine has a to low level of the water or it is runing on muffs.
It also can depend on what kind of charging system for the combustionchamber the engine use. If it is cross scavenging or loop scavenging but not 100% sure.
Running on muffs or in a bucket is not optimal to tune an outboard.

I have noticed for example Japanese brands such as Yamaha and Suzuki from the 70.s and 80.s has this behavior in water on boat and it is not an issue

BUT check the timing plate, it has to move back smooth after reving it up and check the timingadvance so it is set correct.
How is the fuel air mixture set? Should be 1-1,5 turn out from seated it maybe is set to rich
If to lean it usually pop and die when reving it up.

I might be wrong but for me this engine has no big issue.

 

[pnwboat]

I don't know if this has anything to do with the issue, but take a look at the carburetor itself. Make sure it is the correct one. There should be some casting dates on the carburetor. Usually it's a raised circular shaped mark with the two digits cast in the middle. Usually just the last two digits of the year. 87 would be a 1987, 92 would be 1992. You should haves casting dates close to the date of your motor.

Check to see if you have any vacuum leaks. With the motor at idle, spray some carburetor cleaner around the seams where the base of the carburetor bolts to the motor, around the vacuum hoses, the carburetor adapter etc. If the idle speed changes while you're spraying, this may indicate an air leak at that spot. Be careful, some of the overspray may get sucked directly into the mouth of the carburetor causing a change in idle speed and giving you a false indication. Also, some brands of carb cleaner are very good at removing paint.

 

[Frank Acampora]

Agree with Nordin! What you are experiencing is known as Four Cycling. It happens a lot in 2 cycle engines when you goose the throttle under no load and return to neutral quickly. The engine is firing every other revolution instead of each revolution and thus sounds like it is "galloping." Actually it is too rich from high speed collected fuel. As it clears itself it returns to normal. When you choke it you slow it down and it clears itself differently.

In fact, when I was heavy into model airplanes we would sometimes induce four cycling by regulating fuel flow. Set it rich enough and the glow plug fires every other revolution.

You probably don't have an air leak or a carb problem.